1. Field of the Invention
The present invention relates to a surface inspection apparatus and method. More particularly, the present invention relates to a surface inspection apparatus and method in which precision in photoelectrically detecting defects can be high.
2. Description Related to the Prior Art
A surface inspection apparatus inspects a surface of a film sample traveling continuously, and detects defects. A light source in the surface inspection apparatus emits a detection laser beam to the film sample. Light receivers receive the detection laser beam transmitted or reflected by the film sample. If a defect is present on the film sample in a streak form or the like, the defect scatters the detection laser beam to create scattered light. The light receivers receive the scattered light, and generate an output signal from which the defect is detected. According to types of the defect, there are differences in a direction of scattering the scattered light at the defect. For example, a scratch defect has a streak form or elliptical form extending in a longitudinal direction of the film sample. The scattered light from the scratch defect scatters in a film width direction of the film sample.
According to the surface inspection apparatus and a sensor assembly of JP-A 5-215697, the light receivers are arranged in the longitudinal direction and the film width direction of the film sample. The defect on the film sample is detected according to a location of the light receivers of entry of the detection laser beam and light amount information of a light amount of the detection laser beam being received. Types of the defect are detected among a retracting defect and plane surface defect, and among various types of retracting defects, such as scratch defect, pit defect, crack defect and the like. For example, a scratch defect is detected if the detection laser beam is received by one of the light receivers positioned in the film width direction of the film sample.
A sensor array or multiple photomultiplier is available in the field of photo detection, and includes arrays of photomultiplier tubes. In JP-A 5-215697, the photomultiplier tubes are typically used in which the light receivers are arranged in both of the longitudinal direction and the film width direction of the film sample. Voltage for application for the photomultiplier tubes is equal in the multiple photomultiplier. There occurs a difference in sensitivity between the photomultiplier tubes. Even the scattered light of an equal light amount is received, differences will occur in the light amount information of the detection due to the sensitivity difference. Precision in the abnormality detection is considerably low.
In JP-A 5-215697, there is no discernment of the detection laser beam received by the light receivers among statuses including a main output beam normally reflected by the film sample or the scattered light scattered by the defect on the film sample. An output signal from the light receivers upon receiving the main output beam is also used in the abnormality detection. Even when no defect is present on the film sample, it is likely that presence of a defect is detected erroneously according to the output signal from the light receivers upon receiving the main output beam. Precision in the surface inspection is low.